Automatic toothpaste dispenser

I apologize in advance if this is in the incorrect forum, but I really couldn't find anywhere concerning designing, I figured it would be closest to engineering (is an engineering course...)

Anyway, we are supposed to design concepts for an automatic toothpaste dispenser, and I was planning on modeling mine after an automatic soap dispenser (similar to the ones seen in many public bathrooms) where the dispenser is triggered by a sensor. I am trying to research the interworkings of these products, but find it hard to sort through all of the advertising garbage that google spits at you. It would seem to me that it is simply the sensor triggers some sort of arm that would push against the 'bag' of soap, which causes some soap to be pushed out the bottom. I am curious to know if anyone has any recommendations/ideas on the interaction between sensor and the actual force being applied to the toothpaste tube (in my case). Maybe the sensor causes a switch to turn on a circuit that turns on a motor instantaneously that forces an arm to move and return quickly? It seems like there would be a more simple method, that I am just not thinking of clearly.

I usually get some good responses from this site, and I feel like this is a very creative problem that could have some good hints. I really want to come up with the actual concept by myself, but just hints or tips of ways to make something like this work would be great (or maybe a link to a site with some good information!)